Military and other conventional radio networks may be short on frequencies and long on the need to pre-plan frequency requirements before deployments. This problem has been addressed by creating radio systems that are self-organizing in frequency and time. Such a system would first survey the frequencies available upon deployment at a location, then self-organize among the radios at that location to use the frequencies available. In order to prevent interference to and from friendly users and/or prevent interference from unfriendly users, ongoing spectrum surveillance is then required to “see and avoid” other friendly users which appear on the chosen frequencies after the radio begins transmission.
In a fashion somewhat analogous to ordinary conversation, in a radio system one cannot hear clearly when one is talking on the same frequency and one cannot clearly hear one talker when two talkers are on the same frequency. Moreover, radio signals are of widely varying strengths. One especially cannot hear a weak talker when a strong talker is on the same frequency. Moreover, not all users use a frequency all the time. Moreover, in a radio network nearby transmitters even if on different, but nearby, frequencies often emit enough unintended noise in adjacent, or nearby, channels to overwhelm weak signals from distant users on the correct frequency.
Accordingly, in the design of a radio communications system it is common to plan for the operation of the radio system in a band or bands of the frequency spectrum which are licensed in a particular geographic area of interest using a particular format for the over-the-air signal which is acceptable to the licensing authority for a particular category of user. Before actual operation the user obtains a license from the licensing authority allowing the user to operate on a particular frequency, or frequencies, at a specific location, perhaps with a specific antenna height, probably with a power limitation, using a particular over-the-air format. This licensing process is designed to coordinate the use of the spectrum between users and prevent interference by one user with another.
Mobile military deployments in a friendly environment typically are assigned by the administrative authority to large bands of frequencies reserved for military use. Within these bands the military administers its own frequency assignments to a greater extent than that permitted civilian users, but the frequency coordination problem is no less complex. The military planner, while not using a licensing procedure, is confronted with the same planning problem. The problem is exacerbated by the use of more and more radio equipment and the need for faster and faster deployments and military response times. The problem is further complicated with foreign deployments and the need to coordinate spectrum with other countries' military forces, and friendly foreign civilian users.
It is conventional in military applications to listen to enemy transmissions. It is also conventional in civilian applications to characterize the interference environment. For example, at sites that test radio equipment for undesired emissions, it is common to catalog other interfering emissions in the area. It is also conventional to listen before talking. Human radio operators are perhaps the best example, but automatic systems in the ISM band do this as well, and Carrier Sense Multiple Access (CSMA) systems obviously listen before individual transmissions. In frequency “hopping” systems it is also conventional to avoid certain frequencies with conflicts which are known a priori. However, systems do not conventionally operate in which the system self-organizes in frequency, and dynamically changes its own frequency assignments based on ongoing surveillance, while giving the appearance of continuous operation. The apparently continuous waveform of the inventive radio system will require coordinated periods of silence system-wide to listen for non-system users, and new system users. System wide silence is preferred on a band or sub-band of frequencies within the operating band which is sufficiently wide to permit effective surveillance and detection of non-system users or non-system interference, without interference from, perhaps strong, system users adjacent to the silenced band of frequencies. The periods of silence may be moved cryptographically in time and frequency to improve performance of the system.
Accordingly, there is a need for a radio system and method that self-organizes in frequency and in which a repeated silent period may be used to detect traffic on the frequency band that is being used by the radio network. There is also a need for a radio system and method in which a silent period may be repeatedly used over a sub-band of the band of frequencies on which a radio system is operating to detect traffic on the sub-band.
It would be desirable to provide a system and/or method that provides one or more of these or other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the aforementioned needs.